Topic Area: 9c. Remediation and Management of Petroleum Hydrocarbon-Contaminated Sites

Formatted Title:

Enhanced Hydrocarbon Biodegradation via Soil Vapor Extraction (SVE) System Operation

Background/Objectives:

Soil vapor extraction (SVE) is a common remediation technology for sites contaminated with petroleum light non-aqueous phase liquid (LNAPL). The effectiveness of SVE systems is typically evaluated by monitoring the hydrocarbon vapor concentration in the vapor system effluent and calculating the mass removal of hydrocarbons based on this vapor concentration and the system total vapor extraction flow rate. SVE systems also pull atmospheric air into the subsurface, increasing the oxygen available in the LNAPL source area and potentially enhancing aerobic petroleum biodegradation. However, this enhanced biodegradation is typically not considered when evaluating the effectiveness of the SVE system and quantifying mass removal rates.

Approach/Activities:

We have developed a tool to calculate the petroleum biodegradation attributable to decreased oxygen concentrations and increased methane and carbon dioxide concentrations measured in SVE system effluent gas. The magnitude of petroleum biodegradation associated with measured methane in the effluent is calculated based on the stoichiometry for methanogenic biodegradation of petroleum, while the magnitude of petroleum biodegradation associated with depletion of oxygen and increase in carbon dioxide in the effluent is calculated based on the stoichiometry for aerobic biodegradation of petroleum. To evaluate the magnitude of biodegradation associated with SVE, we have applied these calculations to effluent monitoring records from five (5) sites with long-term SVE systems. Additionally, carbon dioxide and oxygen concentration ratios were compared to the expected stoichiometry of complete hydrocarbon biodegradation as a line of evidence to evaluate whether effluent gas concentrations are indicative of expected biodegradation patterns.

Alexandra Farnell

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Enhanced Hydrocarbon Biodegradation via Soil Vapor Extraction (SVE) System Operation